1. Field of the Invention
This invention relates to a wireless communication system and to a method of making the system. More particularly, the invention relates to a wireless communication system, such as for portable telephones, on a chip.
2. Discussion of the Related Art
Emerging applications for portable wireless voice and data communications (wireless internet) systems require increased data rates and functionality. Meeting cost and performance goals requires careful attention to system level design and partitioning such that appropriate technologies are employed in cost-effective implementations. It is believed that optimum implementations will employ a mixture of GaAs and silicon integrated circuits as well as high-performance miniaturized passive components.
As the existing RF spectrum becomes more and more crowded, new radio frequency integrated circuit (RFIC) capabilities will be required to implement power and spectrally efficient digital modulation and demodulation schemes needed by new wireless systems.
Typical radio architectures and transceiver sub-circuits which have been integrated are described by L. M. Burns, xe2x80x9cApplications for GaAs and Silicon ICs in Next Generation Wireless Communication-Systems,xe2x80x9d Technical Digest, 16th Annual GaAs IC Symposium, p. 155-158, 1994, which publication is incorporated herein by reference.
A circuit from the Burns et al publication is provided in FIG. 1. With reference to FIG. 1, there is shown Plessey""s Frequency Hopping Spread Spectrum transceiver, which operates in the 2.4 GHz GSM band, and which is a good example of a wireless system for use with the present invention. The system has a base double conversion super heterodyne architecture with only two master oscillators which enables fast switching between transmit and receive modes. GaAs is used in the IC 20 containing the low noise amplifier (LNA), up and down converting mixers, switches for transmit/receive (T/R) and antenna switching 22 and one of the voltage controlled oscillators (VCO""s) 23. The second IC 30 contains the downconverting mixer, intermediate frequency (IF) limiting amplifier, received signal strength indicator (RSSI) and frequency discriminator. This IC 30 is fabricated using a high speed silicon bipolar process.
A third IC 40, fabricated using the same high speed silicon bipolar process, contains high frequency prescalers, dividers and the second VCO. Three phase locked loops (PLLs) 50,52,54 fabricated in 1 xcexcm CMOS are used to set the frequencies of the two master oscillators. A variety of miniature, high performance passive filters are also used. A high-Q ceramic resonator filter is used to band limit the transmit/receive (TX/RX) signals. Surface acoustic wave (SAW) filters are used in the first and second IF strips to provide needed selectivity while maintaining good group delay characteristics. A simple gaussian LC lowpass filter is used to pulse shape the transmitted signal to implement GFSK modulation.
Another RF transmission/reception circuit from the Burns et al. publication which has been integrated is shown in FIG. 2. With reference to FIG. 2, the wireless system shown is the National Semiconductor DECT transceiver. This transceiver contains many of the same functional building blocks as the Plessey example in FIG. 1. The transceiver operates in the 1.88-1.90 GHz band. Almost all of the ICs in this design are fabricated in National""s silicon BiCMOS IC process. The most notable exception is the GaAs power amplifier. Although the silicon downconverter/mixer has a relatively high aggregate noise figure of 8.7 dB, this is adequate to meet DECT specifications. A single conversion, superheterodyne receiver is used. The DECT transceiver also uses gaussian filtering on the transmitted data stream. However, the National transceiver filters the bit stream with an on-chip gaussian lowpass filter based on a ROM look-up table.
Optical transceiver applications have also been integrated. See, for example, Rodrigo et al, xe2x80x9cAlGaAs/GaAs HEMT 5-12 GHz Integrated System for an Optical Receiver,xe2x80x9d Proceedings of the 1998 IEEE International Symposium on Circuits and Systems, vol. 2, p. 312-315, 1998, which publication is incorporated herein by reference. A system from Rodrigo et al is illustrated in FIG. 3. The circuit includes an input network 80 to emulate the photodiode function, a pre-amplifier 82, an automatic gain control (AGC) unit 84, two gain stages 86, the comparator 87 and the output buffer 88.
Microwave transmission and reception circuits have also been integrated. There are two basic types of integrated circuit structures for microwave transmission/reception systems: monolithic microwave integrated circuits (MMIC) and microwave integrated circuits (MIC). However, these structures have basic problems. The MMIC die is large because needed microwave matching and filter circuits occupy a large area which results in high cost. The MIC die is also large because conventional MIC""s consist of single-layer circuits. In response to these problems, a multilayer microwave integrated circuit (MuMIC) was introduced by Matsushita Electronics as described by N. Yoshikawa et al in xe2x80x9cMultilayer Microwave Integrated circuit Technology for GaAs Power Amplifier of Personal Communication System,xe2x80x9d Technical Digest of 1995 International Solid State Circuit Conference, p. 190-191, 365, 1995, which publication is incorporated herein by reference. The MuMIC uses a multilayer substrate formed of low temperature co-fired ceramics.
To reduce the size and weight of mobile telephones, tape automated bonding (TAB) has been used in a multilayer integrated circuit configuration to assemble a 900 MHz-band GaAs multichip power amplifier module for a Mitsubishi Electric transmitter as described in Y. Notani et al, xe2x80x9cGaAs Multi-chip Power Amplifier Module using a Multi-layer TAB Tape,xe2x80x9d Technical Digest, 1994 16th Annual GaAs IC symposium, p. 145-148, 1994, which publication is incorporated herein by reference.
Another example of a radio frequency integrated circuit (RFIC) is described by McGrath et al in xe2x80x9cA 1.9-GHz GaAs Chip Set for the Personal Handyphone System,xe2x80x9d IEEE Transactions on Microwave Theory and Techniques, vol. 43, no. 7, p. 1733-1744, 1995, which publication is incorporated herein by reference. The McGrath et al publication includes chip, partition, design and performance of each sub-function relative to requirements imposed by an air interface.
Although the articles discussed above illustrate attempts at integrating many of the components of a wireless communication system using several ICs and passive components, they still require numerous integrated circuits and/or large die areas. Accordingly, further integration and size reduction is required, particularly for wireless communications devices, such as cellular telephones.
The present invention provides structure for enhanced compactness and miniaturization which permits further integration and simplified interconnection of the components of a wireless communication device, such as those for a portable telephone.
In accordance with the present invention, there is provided a wireless communication device comprising a carrier having a top and a bottom, and a plurality of integrated circuit components located on the top and bottom of the carrier for transmitting, receiving and processing wireless communication signals. At least one passageway extends through the carrier, and conductive material extends through the passageway for electrically interconnecting the integrated circuit components located on the top and bottom of the carrier.
The present invention also provides a method of forming a wireless communication device comprising the steps of providing a carrier having a top and a bottom surface and forming holes through the carrier between the top or bottom surfaces. Integrated circuitry is formed on the top and bottom surfaces of the carrier as mounted chips or circuit elements fabricated within the carrier for transmitting, receiving and processing wireless communication signals. The holes are filled with conductive material to interconnect the integrated circuitry on both sides of the carrier.
The carrier is preferably formed of silicon. Further, the wireless communication signals may represent voice, data and/or images. In one embodiment, the wireless communication system is a portable telephone.
As used herein, the term xe2x80x9ccarrierxe2x80x9d means any substrate structure, whether or not part of a semiconductor wafer, for supporting integrated circuit (IC) components on opposite sides thereof. The substrate may include one or more layers of materials on opposite sides which are fabricated to define the components and electrical circuity of a wireless communications device. The integrated circuitry is formed as chips mountable on the carrier and/or circuit element fabricated within the carrier surfaces. Functionally, the substrate may be capable of having holes formed therethrough, preferably by etching. The holes are provided as passageways for conductive material to interconnect integrated circuit (IC) components on opposite sides of the substrate. As noted, components of the communication device are fabricated directly on the carrier and/or are formed as integrated circuit chips mounted on the carrier.
Suitable compositions for the carrier include silicon, SiGe, GaAs, GaAlAs, SiC and mixtures thereof. As noted above, silicon is preferred.
The cost of SiGe chips are claimed to be lower than that of GaAs chips. See J. M. Moniz, xe2x80x9cIs SiGe the Future of GaAs for RF Applications?,xe2x80x9d Technical Digest, 997 19th Annual GaAs IC Symposium, p. 229-231, 1997, which publication is incorporated herein by reference.
The use of silicon as a carrier has many advantages over the low-temperature co-fired ceramic carrier used in the multilayer microwave integrated circuit (MuMIC) described in the Yoshikawa et al publication, supra. For example, fabrication of many different types of passive components, such as filters, resonators, and matching networks, and interconnection between active chips and other components can be accomplished by ordinary integrated circuit processing techniques directly on silicon carrier. When packaged, there will be no mismatch in thermal expansion coefficients between the active silicon chips and the silicon carrier to which the chips are mounted. Further silicon is readily available. Also, for the instant application, reject silicon substrates from other device fabrication, such as microwave or RF front-end processing, can be used as carriers.
The fabrication of the wireless communication system in this compact structure is enabled by novel holes in the silicon carrier for feedthroughs and also unique coaxial feedthroughs.
In order to simplify and reduce the processing complexity of microwave GaAs chips, circuits which require large area such as matching and filter circuits are fabricated directly on the silicon carrier.
Combining microwave frequency GaAs chips and radio frequency chips fabricates on silicon onto a silicon carrier in accordance with the instant invention provides for a more tightly integrated product offering higher performance and lower cost.